This invention relates to the use of light in determining the characteristics of objects, especially dimensional information about relatively small features in flat-panel cathode-ray tube (xe2x80x9cCRTxe2x80x9d) displays.
A flat-panel CRT display is typically formed with an electron-emitting device and a light-emitting device situated opposite the electron-emitting device. In a flat-panel CRT display of the gated field-emission type (xe2x80x9cfield-emission displayxe2x80x9d), the electron-emitting device contains a baseplate, a lower level of emitter electrodes overlying the baseplate""s interior surface, a dielectric layer overlying the emitter electrodes, and an upper level of control (or gate) electrodes extending over the dielectric layer. Electron-emissive elements are situated in openings in the dielectric layer and are exposed through openings in the control electrodes.
The light-emitting device in a field-emission display (xe2x80x9cFEDxe2x80x9d) contains a transparent faceplate, an anode that overlies the faceplate""s interior surface, and an array of light-emitting regions also overlying the faceplate""s interior surface. During operation of the FED, electrons are emitting from selected electron-emissive elements and are attracted by the anode to the light-emitting device. Upon reaching the light-emitting device, the electrons strike corresponding light-emissive regions and cause them to emit light that produces an image on the faceplate""s exterior surface.
For a flat-panel display to operate properly and provide a distinct image, the dimensions in certain parts of the display need to be controlled carefully. Controlling these dimensions typically entails measuring their values. It is often desirable that measurement be performed as the display portion having the dimensions is being fabricated.
In some cases, the dimensions that need to be measured carefully are quite small. For example, in an FED, the diameters of the openings that contain the electron-emissive elements are commonly on the order of 0.1 xcexcm. Due to the small diameter value, highly sophisticated equipment such as a scanning electron microscope or an atomic force microscope is conventionally employed to measure the opening diameters. A relatively large amount of time is typically needed for setting up the equipment to make the measurements, including replacement of worn-out components such as measurement tips, and for subsequently analyzing the accumulated data. It is difficult to perform measurement with such equipment as the openings are being created.
Furthermore, the scanning electron microscope and atomic force microscope each often have a relatively small amount of chamber volume for receiving a specimen that is to be examined. To perform a measurement, a good specimen must commonly be broken into pieces small enough to be placed in the chamber volume. It is desirable to have a simple non-intrusive analytical technique and system for measuring small dimensions, such as the diameters of small openings, in objects such as components of flat-panel displays. It is also desirable that the analytical technique and system be of such a nature that the measurement can be made during the fabrication of the feature having the dimensions being measured.
The present invention furnishes a group of analytical techniques and systems in which scattered and/or transmitted light is employed in determining certain characteristics of objects such as partially or completely fabricated components of flat-panel displays. The characteristics include the average diameters of openings in the objects.
The openings can be quite small. The average opening diameter is typically less than the wavelength of the scattered and/or transmitted light utilized in determining, i.e., measuring, the opening diameter. The scattered and/or transmitted light typically includes visible light. Inasmuch as visible light ranges in wavelength from approximately 0.4 xcexcm to approximately 0.7 xcexcm, the present light-scattering or light-transmission technique can be utilized to measure opening diameters of less than 0.4 xcexcm. An average opening diameter in the vicinity of 0.1 xcexcm or less can readily be measured in accordance with the invention. Also, the diameter measurement can be performed as the openings are being created. The present analytical techniques and systems are thus highly beneficial.
More particularly, in accordance with one aspect of the invention, light which scatters as it propagates into openings in an object is collected to produce a light-collection signal representative of the intensity of the scattered light. The scattered light includes light which undergoes diffraction in propagating into the openings in the object. The scattered light may be concentrated at one or more wavelengths or may be distributed across a wavelength band. In either case, the scattered light used to produce the light-collection signal is of wavelength greater than or equal to a principal wavelength value. The average diameter of the openings is less than the principal wavelength value, preferably less than one half the principal wavelength value. Hence, the scattered light used to produce the light-collection signal is of wavelength greater than, or equal to, the average opening diameter. The light-collection signal for the scattered light is evaluated to determine dimensional information about the openings. The dimensional information typically includes the average opening diameter.
In accordance with another aspect of the invention, light transmitted through openings in an object is collected to produce a light-collection signal representative of the intensity of the transmitted light. The transmitted light used to produce the light-collection signal has the same wavelength characteristics relative to the openings as the scattered light utilized in the first-mentioned aspect of the invention. That is, the transmitted light used to produce the light-collection signal is of wavelength greater than, or equal to, the average diameter of the openings. The light-collection signal for the transmitted light is evaluated to determine dimensional information about the openings. Once again, the dimensional information typically includes the average opening diameter.
In the first-mentioned aspect of the invention, additional light whose wavelength is too small to be employed in producing the light-collection signal is typically scattered in propagating into the openings. Similarly, additional light whose wavelength is too small to be employed in producing the light-collection signal is typically transmitted through the openings in the second-mentioned aspect of the invention. For simplicity, the additional (unused) scattered and transmitted light is not mentioned further in this general disclosure of the invention.
An analytical system that implements the light-scattering or light-transmission technique of the invention contains a light-emitting structure, a light-collecting structure, and a processor. The light-emitting structure provides light which is transmitted through the openings or/and undergoes scattering in being propagated into the openings. The light-collecting structure collects the transmitted or scattered light, and provides the light-collection signal. The processor evaluates the light-collection signal to determine the desired dimensional information.
The principles of the invention can be applied in various ways to determine dimensional information other than the average diameter of the openings. For example, when the openings extend through a layer of the object, both scattered and transmitted light having the above-described wavelength characteristics relative to the average opening diameter can be collected to produce light-collection signals respectively representative of the intensities of the scattered and transmitted light. The light-collection signals are then evaluated, typically by a comparison procedure, to determine the average thickness of the layer. An analytical system that determines the average layer thickness contains a light-emitting structure, a light-collecting structure, and a processor operable generally in the manner described above except that the resulting dimensional information is the average layer thickness.
In accordance with a further aspect of the invention, light is directed towards an object, such as part of a flat-panel display, having a group of generally parallel first lines and a group of generally parallel second lines that cross the first lines. Light is diffracted off the first lines to produce a diffraction pattern characteristic of the first lines. Light is similarly diffracted off the second lines to produce a diffraction pattern characteristic of the second lines. The diffraction patterns are examined to determine certain characteristics of the lines. As an example, when an abnormality, such as a defect, occurs in one or both of the groups of lines, each group of lines having the abnormality can be determined by comparing the diffraction patterns.
The present techniques and systems for determining characteristics of objects are quite simple. Little time is needed for equipment setup. The systems of the invention normally perform the necessary data analysis automatically. The present analytical techniques are non-intrusive. There is typically no need to break up a good specimen, especially when the specimen is a component of a flat-panel display, into smaller pieces or to otherwise damage a specimen in order to determine the specimen""s characteristics which are determinable in accordance with the invention. The characteristics can normally be determined across the entire specimen without damaging it.
The analytical techniques of the invention can be performed during the fabrication of the feature that is to be analyzed according to the invention. The measurement accuracy achieved with the present analytical systems is typically better than that achieved with electron microscopes. Consequently, the invention provides a large advance over the prior art.